0fb570338f
- Trigger noise floor calibration every 2s and AGC reset every 30s in main loop. - Reorder loop to match Dispatcher: calibrate + radio.loop() before AGC reset and recvRaw() so RSSI is never sampled right after startReceive(). - Update protocol doc with calibration intervals and typical noise floor range. - Variant platformio.ini updates (heltec_v3, rak4631).
165 lines
6.1 KiB
Markdown
165 lines
6.1 KiB
Markdown
# MeshCore KISS Modem Protocol
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Serial protocol for the KISS modem firmware. Enables sending/receiving MeshCore packets over LoRa and cryptographic operations using the modem's identity.
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## Serial Configuration
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115200 baud, 8N1, no flow control.
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## Frame Format
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Standard KISS framing with byte stuffing.
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| Byte | Name | Description |
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|------|------|-------------|
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| `0xC0` | FEND | Frame delimiter |
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| `0xDB` | FESC | Escape character |
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| `0xDC` | TFEND | Escaped FEND (FESC + TFEND = 0xC0) |
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| `0xDD` | TFESC | Escaped FESC (FESC + TFESC = 0xDB) |
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```
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┌──────┬─────────┬──────────────┬──────┐
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│ FEND │ Command │ Data (escaped)│ FEND │
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│ 0xC0 │ 1 byte │ 0-510 bytes │ 0xC0 │
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└──────┴─────────┴──────────────┴──────┘
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```
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Maximum unescaped frame size: 512 bytes.
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## Commands
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Command and response codes below are taken from `examples/kiss_modem/KissModem.h` and the switch in `KissModem::processFrame()`.
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### Request Commands (Host → Modem)
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| Command | Value | Data |
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|---------|-------|------|
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| `CMD_DATA` | `0x00` | Packet (2-255 bytes) |
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| `CMD_GET_IDENTITY` | `0x01` | - |
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| `CMD_GET_RANDOM` | `0x02` | Length (1 byte, 1-64) |
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| `CMD_VERIFY_SIGNATURE` | `0x03` | PubKey (32) + Signature (64) + Data |
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| `CMD_SIGN_DATA` | `0x04` | Data to sign |
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| `CMD_ENCRYPT_DATA` | `0x05` | Key (32) + Plaintext |
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| `CMD_DECRYPT_DATA` | `0x06` | Key (32) + MAC (2) + Ciphertext |
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| `CMD_KEY_EXCHANGE` | `0x07` | Remote PubKey (32) |
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| `CMD_HASH` | `0x08` | Data to hash |
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| `CMD_SET_RADIO` | `0x09` | Freq (4) + BW (4) + SF (1) + CR (1) |
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| `CMD_SET_TX_POWER` | `0x0A` | Power dBm (1) |
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| *reserved* | `0x0B` | *(not implemented)* |
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| `CMD_GET_RADIO` | `0x0C` | - |
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| `CMD_GET_TX_POWER` | `0x0D` | - |
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| *reserved* | `0x0E` | *(not implemented)* |
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| `CMD_GET_VERSION` | `0x0F` | - |
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| `CMD_GET_CURRENT_RSSI` | `0x10` | - |
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| `CMD_IS_CHANNEL_BUSY` | `0x11` | - |
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| `CMD_GET_AIRTIME` | `0x12` | Packet length (1) |
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| `CMD_GET_NOISE_FLOOR` | `0x13` | - |
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| `CMD_GET_STATS` | `0x14` | - |
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| `CMD_GET_BATTERY` | `0x15` | - |
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| `CMD_PING` | `0x16` | - |
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| `CMD_GET_SENSORS` | `0x17` | Permissions (1) |
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### Response Commands (Modem → Host)
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| Command | Value | Data |
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|---------|-------|------|
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| `CMD_DATA` | `0x00` | SNR (1) + RSSI (1) + Packet |
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| `RESP_IDENTITY` | `0x21` | PubKey (32) |
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| `RESP_RANDOM` | `0x22` | Random bytes (1-64) |
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| `RESP_VERIFY` | `0x23` | Result (1): 0x00=invalid, 0x01=valid |
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| `RESP_SIGNATURE` | `0x24` | Signature (64) |
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| `RESP_ENCRYPTED` | `0x25` | MAC (2) + Ciphertext |
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| `RESP_DECRYPTED` | `0x26` | Plaintext |
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| `RESP_SHARED_SECRET` | `0x27` | Shared secret (32) |
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| `RESP_HASH` | `0x28` | SHA-256 hash (32) |
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| `RESP_OK` | `0x29` | - |
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| `RESP_RADIO` | `0x2A` | Freq (4) + BW (4) + SF (1) + CR (1) |
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| `RESP_TX_POWER` | `0x2B` | Power dBm (1) |
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| *reserved* | `0x2C` | *(not implemented)* |
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| `RESP_VERSION` | `0x2D` | Version (1) + Reserved (1) |
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| `RESP_ERROR` | `0x2E` | Error code (1) |
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| `RESP_TX_DONE` | `0x2F` | Result (1): 0x00=failed, 0x01=success |
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| `RESP_CURRENT_RSSI` | `0x30` | RSSI dBm (1, signed) |
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| `RESP_CHANNEL_BUSY` | `0x31` | Result (1): 0x00=clear, 0x01=busy |
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| `RESP_AIRTIME` | `0x32` | Milliseconds (4) |
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| `RESP_NOISE_FLOOR` | `0x33` | dBm (2, signed) |
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| `RESP_STATS` | `0x34` | RX (4) + TX (4) + Errors (4) |
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| `RESP_BATTERY` | `0x35` | Millivolts (2) |
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| `RESP_PONG` | `0x36` | - |
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| `RESP_SENSORS` | `0x37` | CayenneLPP payload |
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## Error Codes
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| Code | Value | Description |
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|------|-------|-------------|
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| `ERR_INVALID_LENGTH` | `0x01` | Request data too short |
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| `ERR_INVALID_PARAM` | `0x02` | Invalid parameter value |
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| `ERR_NO_CALLBACK` | `0x03` | Feature not available |
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| `ERR_MAC_FAILED` | `0x04` | MAC verification failed |
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| `ERR_UNKNOWN_CMD` | `0x05` | Unknown command |
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| `ERR_ENCRYPT_FAILED` | `0x06` | Encryption failed |
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| `ERR_TX_PENDING` | `0x07` | TX already pending |
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## Data Formats
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### Radio Parameters (CMD_SET_RADIO / RESP_RADIO)
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All values little-endian.
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| Field | Size | Description |
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|-------|------|-------------|
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| Frequency | 4 bytes | Hz (e.g., 869618000) |
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| Bandwidth | 4 bytes | Hz (e.g., 62500) |
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| SF | 1 byte | Spreading factor (5-12) |
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| CR | 1 byte | Coding rate (5-8) |
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### Received Packet (CMD_DATA response)
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| Field | Size | Description |
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|-------|------|-------------|
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| SNR | 1 byte | Signal-to-noise × 4, signed |
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| RSSI | 1 byte | Signal strength dBm, signed |
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| Packet | variable | Raw MeshCore packet |
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### Noise Floor (RESP_NOISE_FLOOR)
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Response to `CMD_GET_NOISE_FLOOR` (0x13). Little-endian.
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| Field | Size | Description |
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|--------------|------|--------------------------------|
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| Noise floor | 2 | int16_t, dBm (signed), e.g. -120 |
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The modem recalibrates the noise floor periodically (every 2 s) from RX samples when idle. The receiver AGC is also reset periodically (every 30 s) so RSSI and noise floor do not drift to the minimum (-120). Typical range after calibration is about -120 to -90 dBm. Values may be 0 or briefly stale until the radio has been in receive mode long enough to collect 64 samples.
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### Stats (RESP_STATS)
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Response to `CMD_GET_STATS` (0x14). All values little-endian.
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| Field | Size | Description |
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|-------|------|-------------|
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| RX | 4 bytes | Packets received |
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| TX | 4 bytes | Packets transmitted |
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| Errors | 4 bytes | Receive errors |
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### Sensor Permissions (CMD_GET_SENSORS)
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| Bit | Value | Description |
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|-----|-------|-------------|
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| 0 | `0x01` | Base (battery) |
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| 1 | `0x02` | Location (GPS) |
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| 2 | `0x04` | Environment (temp, humidity, pressure) |
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Use `0x07` for all permissions.
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### Sensor Data (RESP_SENSORS)
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Data returned in CayenneLPP format. See [CayenneLPP documentation](https://docs.mydevices.com/docs/lorawan/cayenne-lpp) for parsing.
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## Notes
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- Modem generates identity on first boot (stored in flash)
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- SNR values multiplied by 4 for 0.25 dB precision
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- Wait for `RESP_TX_DONE` before sending next packet
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- Sending `CMD_DATA` while TX is pending returns `ERR_TX_PENDING`
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- See [packet_structure.md](./packet_structure.md) for packet format
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